Decomposition begins several minutes after death, with a process called autolysis, or self-digestion. Soon after the heart stops beating, cells become deprived of oxygen, and their acidity increases as the toxic by-products of chemical reactions begin to accumulate inside them. Enzymes start to digest cell membranes and then leak out as the cells break down. This usually begins in the liver, which is enriched in enzymes, and in the brain, which has high water content; eventually, though, all other tissues and organs begin to break down in this way. Damaged blood cells spill out of broken vessels and, aided by gravity, settle in the capillaries and small veins, discolouring the skin. Far from being ‘dead,’ however, a rotting corpse is teeming with life. A growing number of scientists view a rotting corpse as the cornerstone of a vast and complex ecosystem, which emerges soon after death and flourishes and evolves as decomposition proceeds.

Putrefaction is associated with a marked shift from aerobic bacterial species, which require oxygen to grow, to anaerobic ones, which do not. These then feed on the body tissues, fermenting the sugars in them to produce gaseous by-products such as methane, hydrogen sulphide and ammonia, which accumulate within the body, inflating (or ‘bloating’) the abdomen and sometimes other body parts, too. The alkaline environment created by the flies is toxic for beetles and so beetles are largely excluded from feeding on the dead body itself as long as the fly larvae are active. However, many species of rove beetle, carrion beetle and burrowing beetle are still present in the early stages of decomposition because they are active predators of fly larvae, avoiding the alkaline tissues of the corpse. The build up of gas resulting from the intense activity of the multiplying bacteria, creates pressure within the body. This pressure inflates the body and forces fluids out of cells and blood vessels and into the body cavity. Insect activity Bacteria break down tissues and cells, releasing fluids into body cavities. They often respire in the absence of oxygen (anaerobically) and produce various gases including hydrogen sulphide, methane, cadaverine and putrescine as by-products. People might find these gases foul smelling, but they are very attractive to a variety of insects. Lindgren and Bucheli found a scorpionfly, Panorpa nuptialis, feeding on brain fluids through an autopsy incision. Photograph: Natalie LindgrenUltimately, though, decomposition is beneficial for the ecosystem – the microbial biomass within the cadaver decomposition island is greater than in other nearby areas; nematode worms also become more abundant, and plant life more diverse. Further research into how decomposing bodies alter the ecology of their surroundings may provide a new way of finding murder victims whose bodies have been buried in shallow graves. Flies have great powers of dispersal and they rapidly discover bodies, usually* ahead of the beetles. Although they can feed on fluid that exudes from a fresh body, the acidic tissues of a fresh corpse cannot be digested by flies. The activities of the bacteria, and the excretions of fly larvae feeding on exuded fluid, eventually neutralise the acid making the semi-liquid corpse particularly attractive to blowflies, flesh flies and house flies. Even if colonization does occur just after death, estimates based on insects’ age may be inaccurate for another reason. Insects are cold-blooded, and so their growth rate occurs relative to temperature rather than to the calendar. “When using insects to estimate post-mortem interval, we’re actually estimating the age of the maggot and extrapolating from that,” says Bucheli. “We measure insect birth rate by accumulated degree hours [the sum of the average hourly temperature], so if you know the temperature and the growth cycle of a fly, you can estimate the age of a fly within an hour or two.”

If not, time of death estimates based on information about insect colonization can be wildly inaccurate and misleading. Eventually, though, Bucheli believes that combining insect data with microbiology could help to make the estimates more accurate, and possibly provide other valuable information about the circumstances of death. Rodriguez, WC. and Bass, WM. (1985). Decomposition of buried bodies and methods that may aid in their location. Journal of Forensic Sciences. 30: 836-852. Composition notebooks have been used by students for many years, while decomposition notebooks are a relatively new trend. Conclusion Last year, forensic scientist Gulnaz Javan of Alabama State University in Montgomery and her colleagues published the very first study of what they have called the thanatomicrobiome (from thanatos, the Greek word for ‘death’). Composition books are basically the exercise books or notebooks students use to take notes or complete their homework. Decomposition books are a new variation of composition books with new designs and patterns. Key Areas CoveredFlies will arrive at a cadaver almost immediately,” says Bucheli. “We’ll put a body out and three seconds later there’ll be flies laying eggs in the nose.” lactic acid - an organic acid produced in mammals during the breakdown of glucose when oxygen is in short supply.

The speed of the chemical reactions involved doubles with every 10°C rise in temperature, so a cadaver will reach the advanced stage after 16 days at an average daily temperature of 25°C, and after 80 days at an average daily temperature of 5°C.A large volume of body fluids drain from the body at this stage and seep into the surrounding soil. Other insects and mites feed on this material. The study was led by Bucheli’s former Ph.D. student Natalie Lindgren, who placed four cadavers on the Huntsville body farm in 2009, and left them out for a whole year, during which time she returned four times a day to collect the insects that she found on them. The usual suspects were present, but Lindgren also noted four unusual insect-cadaver interactions that had never been documented before, including a scorpionfly that was found feeding on brain fluids through an autopsy wound in the scalp, and a worm found feeding on the dried skin around where the toenails had been, which was previously only known to feed on decaying wood. Her work involves collecting recently deceased bodies from the Dallas-Fort Worth area, and sometimes beyond, and preparing them for their funeral, by washing and embalming them. Embalming involves treating the body with chemicals that slow down the decomposition process, primarily to restore it as closely as possible to its natural state before death. Williams performs this so that family and friends can view their departed loved one at the funeral. Victims of trauma and violent deaths usually need extensive facial reconstruction, a highly skilled and time-consuming task. The so-called gut microbiome is one of the hottest research topics in biology at the moment. Some researchers are convinced that gut bacteria play essential roles in human health and disease, but we still know very little about our make-up of these mysterious microbial passengers, let alone about how they might influence our bodily functions. All of our samples came from criminal cases involving people who died by suicide, homicide, drug overdose, or in traffic accidents,” she explains. “Taking samples this way is really hard, because we have to ask the [bereaved] families to sign our consent forms. That’s a major ethical issue.”